lec38_rec8_phonekeypad.cpp

#include <iostream>
#include<vector>

using namespace std;

void solve(string digits, string output, int index, vector<string> &ans, vector<string> mapping)
{
    // base case
    if (index >= digits.length())
    {
        ans.push_back(output);
        return;
    }

    int number = digits[index] - '0';
    string value = mapping[number];

    for (int i = 0; i < value.length(); i++)
    {
        output.push_back(value[i]);
        solve(digits, output, index + 1, ans, mapping);
        output.pop_back();
    }
}

vector<string> letterCombinations(string digits)
{

    vector<string> ans;
    if (digits.length() <= 0)
        return ans;
    string output;
    int index = 0;
    vector<string> mapping = {" ", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
    solve(digits, output, index, ans, mapping);
    return ans;
}

int main()
{
    string digits="23";
    vector <string> ans = letterCombinations(digits);

    for(int i=0;i<ans.size();i++){
        cout<<ans[i]<<" ";
    }
    cout<<endl;


    return 0;
}